Your neck is turning black due to a condition known as hyperpigmentation. Hyperpigmentation is a harmless skin condition that causes the certain patches of skin to go darker than other areas of surrounding skin. The skin starts to get dark because of the production of excess melanin. Melanin is the skin pigment which gives our skin color. Due to overexposure of the skin to the sun and in order to protect the lower layers of skin from UV the body starts to produce a extra amount of melanin in the exposed area, and this leads to the formation of certain areas in comparison to others. Hyperpigmentation is also known as liver spots or solar lentigines.
The most common remedy you can use to combat this is a prescription cream that contains hydroquinone. The cream helps in bleaching the area and in effect fades the dark patches of skin, by reducing the level of production of melanin. A chemical peel is another intensive technique but should be considered only if the intensity if the dark patch is very high. Some of the easier remedies that you can try are the use of coca butter or aloe vera. Cocoa butter is a home remedy that should be put on the affected area at least once or twice everyday for about a period of two or three weeks in order to be effective. Aloe vera is also very effective and can be used as an alternative to coca butter. Aloe Vera gel can even be applied to the skin directly from the plant, but avoid going out into the sun after applying it. As it may, result in a rash on the back of your neck. Aloe vera is also available in a cream form and generally needs about a two or three week treatment in order to be effective.
answered by M W